U-boot modifications for UART1

I am trying to access UART1 on expansion header. In
order to do so I need to chance the u-boot.bin so as to
configure the pin-mux on expansion header.

I tried looking into previous posts on UART and OMAP TRM
and I guess I know what needs to be changed in u-boot.bin.

But I could not figure out how to get u-boot-main for beagleboard
(Rev. B7), so that I can do necessary changes. Also how to re-compile
u-boot to u-boot.bin once the necessary changes are done.

I am using beagleboard Rev. B7

Any help on above problems will be of great help.

Thanks,
Amit

Have you tried these instructions: http://elinux.org/BeagleBoard#U-Boot